Pursuing Performance

Written
by
Terry McGean
on September 12, 2006 After a mild refresh and shakedown of our 96 9C1 Caprice, it's time to step up the game on the old girl just a bit. The ex-cop car gets some basic performance upgrades and some basic maintenance items in preparation for future upgrades. It's always nice

Some months ago we introduced you to our in-house '96 Chevy Caprice 9C1, better known as a cop car. This specimen of the last fullsize rear wheel drive Chevy is equipped with the vaunted Gen II LT1 engine, displacing 5.7 liters and rated at 260 hp with iron cylinder heads. Our interest in the car was primarily as an urban commuter, battling its way through the mean streets of LA while providing a degree of comfort and utility, along with their well-known durability. We selected an LT1 Caprice specifically because of the impressive performance these cars deliver, and since mechanically the 9C1 is nearly identical to the Impala SS of the same era, aftermarket support is available to make it even better.

The time lapse between our introduction of the car and now was due primarily to an extended "shakedown" period, which shook out a steady stream of maladies. Since our car had 175,000 miles when purchased (the engine was replaced with a GM service long-block at 106,000, as was the trans), niggling problems like leaky coolant hoses, burned-out fan relays, and fried ignition parts are expected. But now that the car has provided about 10,000 miles of relatively trouble-free motoring, it's time to turn up the heat.

For the initial thrashing, we strapped our retiree to the Superflow chassis dyno at Westech Performance Group in Mira Loma, California. Rather than throwing a pile of go-fast parts at the high-mileage cruiser, we opted instead for simple tweaks to monitor the car's reaction to ensure the old enforcer is up to the task. If the car responds favorably to the basics, we'll take it as an indication that it's safe to venture on to more serious hardware.

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1 We wanted to make sure the Caprice's lubricants and filters were up to snuff prior to hitting the dyno, to ensure that we weren't introducing other variables into the equation. Besides, the dyno can give a car a real workout, so having fresh fluids is always a good idea. To begin, we used standard Valvoline 5W30 (factory spec) along with a K&N oil filter. The fuel filter was also replaced with a Fram service replacement part.

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2The ignition parts on our Chevy were also well worn, so we swapped in a fresh set of stock-spec AC plugs and a set of MSD plug wires. The wires for the LT1 are somewhat unusual since all Gen II small-blocks use the Opti-Spark ignition system, which is based in a distributor mounted behind the water pump. The task of changing these wires looks deceptively simple, but is actually a major chore, since the wires are routed behind the front accessory drive components and behind the exhaust manifolds in steel looms. It's worth doing on high-mileage cars, though, since this routing allows the engine's heat to take its toll on the LT1's ignition wires.

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3 This being the first trip to the rollers for the Caprice, we wanted to establish a solid baseline. The first pulls were made as the car came off the street--210-degree coolant, 91-octane fuel, and with all factory air intake and exhaust pieces in place. The Caprice has an excellent cooling system, but the factory programmed the electric fans to stay off until the coolant reaches nearly 225 degrees to keep idle emissions clean. This is reflected in the temp gauge as the needle reaches just shy of the three-quarters mark. When the needle sweeps past the straight-up point (typical for non-highway driving), performance falls off substantially judging by seat-of-the-pants input. Our first pulls were made at around 210 degrees, and showed 217 hp and 276 lb-ft.

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4 There are several means of activating the cooling fans at lower temps, including computer reflashing and aftermarket programmer devices. Both are effective, but we decided to take a more mechanical approach by using one of Jet Performance's fan controller switches. The switch comes with wiring to tap into the factory harness and triggers the fans at a lower temp, which in turn allows the engine to run closer to the temp dictated by the thermostat, in this case around 195 degrees. This simple change bumped power up to 222 while torque climbed to 280 lb-ft.

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5 Lowering the fan switching temp may cause the fans to turn on frequently, as the coolant will still be fairly warm thanks to the stock thermostat. The Gen II small-blocks use a uniquely designed thermostat, and while replacements are readily available, all the ones we found at the local parts store were for the stock temperature. Fortunately, the aftermarket offers cooler T-stats for the LT1, so we sourced one from Jet and tried again. Lowering the coolant temp further should continue to boost power, and the next round of pulls confirmed this as we gained an additional 2 hp. We suspect that this change may normally be worth a little more, as our coolant was already fairly warm from previous tests.

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6 Another area often compromised on late-model vehicles is the air cleaner and its ducting. Since auto manufacturers have to subject their vehicles to drive-by noise tests, most air cleaners are baffled to reduce intake "roar"--the sound your mom's station wagon used to make when you flipped the air cleaner lid over. The LT1 Caprice seemed strangled judging by the look of its stock air intake setup. The filter box itself is fed by a small, oval inlet that faces the back of the headlamps and the duct to the mass-airflow sensor (MAF) has a huge resonance chamber with offset inlet and outlet connections. Another resonance chamber is mounted atop the intake manifold, though it doesn't seem to obstruct airflow. We figured a more direct shot to the throttle body would have to help output at least a little.

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7 As a trial experiment, we pulled the lid off of the filter box and faced it forward so it became the inlet to the intake tract. We stuck the stock paper filter element in it and made a pull, showing an instant gain of another 3 hp, and this was with the resonance baffle still in place. We were onto something.

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8 We started scheming to create a high-flow air intake setup, with visions of drilled filter boxes and 3-inch exhaust tubing dancing in our heads. Of course, we also wanted to use a high-flow aftermarket filter, and that's when we learned that K&N actually offers a complete cold-air kit for the Caprice. Actually, this FIPK (Fuel Injection Performance Kit) was developed for the Impala SS, but the hardware is identical on the cop-spec Caprice, so we ordered it up. This kit includes a new filter box, which seals to the hood to keep out hot engine-bay air. It also uses a conical filter rather than the stock panel-type, and it even includes a tube to replace the resonance baffle.

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9 Installation is relatively simple. The stock filter box is removed, which is a simple matter of a couple screws and a few snap-fit connections at the base. The K&N box then attaches to the same mounting points and includes a separate filter for the hose that feeds the engine's air injection pump, which was originally attached to the stock airbox. The filter and tube attach to the box, and the tube is then connected to the stock MAF. When it was all said and done, the K&N kit boosted power to 235 hp and 290 lb-ft of torque.

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10After the dyno test was over, we realized there was another simple trick up our sleeves for the Caprice that should have been tested. The throttle body used on LT1s (like the Tuned-Port engines before them) has a small passage inside for coolant, which is fed via a small hose that taps into the cooling system. The purpose of this arrangement is to prevent ice from accumulating on the throttle blades during cold-climate startups, but the rest of the time it just adds heat to the incoming air. By simply bypassing the coolant connections on the throttle body (connect hose A to hose B), the heat is eliminated--a change reputed to be worth around 3-5 hp in many cases. We'll try this out next time we hit the rollers.

Injector Detector

One of the latest additions to the ever-expanding arsenal of automotive test equipment at Westech Performance Group is the ASNU fuel-injector analyzer. The ASNU rig is intended to provide automotive service centers a means of determining the performance of each injector, allowing technicians to pinpoint defective components by testing them individually under a number of conditions. The rig can test up to eight injectors at a time and provides the ability to vary fuel pressure and injector pulse width, meanwhile allowing the technician to visually observe the injector's spray pattern and compare delivery rates between the injectors in a set. Injectors can be tested for static performance (held open) or dynamic performance (pulsed). There are also programs to simulate typical driving operation, and the rig is capable of simulating engine operation up to 10,000 rpm if so desired. Once the injectors have been tested, the ASNU can also be used to clean them using its patented ultrasonic treatment process. As the name implies, most used injectors can be returned to "as-new" performance using this apparatus.

Although the ASNU was developed for service work, it is obviously an excellent tool for performance tuning and diagnostic work. Our Caprice had fairly new injectors, so we observed a set of Mustang injectors going through the process.